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Abstract: The effects of two different halogen dopants (bromine and iodine) at different concentrations on the higher frequency modes (the so-called G and G′ bands) of the Raman spectra of double-wall carbon nanotube (DWCNT) “buckypaper” are investigated. The effects of dopants on different DWCNT configurations (metallic inner/semiconducting outer and vice versa) are studied by changing the laser excitation energy. The doping causes the loss of the Breit–Wigner–Fano line shape and the appearance of less metallic behavior. An increase of the relative intensity of the G+ band, which is more sensitive for the outer metallic tubes, is clearly observed with increasing Br2 concentration in the sample. By analysis of the G+ band and the G′ band it is possible to measure the changes in the electron–phonon coupling, due to the charge-transfer between the dopant (Br2 or I2) and the tubes in the DWCNT. The doping effect causes an upshift of the G+ band and a suppression of the contribution of the inner tubes to the G′ band signal and as a consequence, the observed G′ band is dominated by the contribution from the outer tubes. [Copyright &y& Elsevier]

The structure of bromine residue compounds was investigated by X-ray absorption fine structure (XAFS) in order to interpret where and how bromine is present in carbons with different degrees of graphitization. The residue compounds can be classified into three groups, as obtained from X-ray absorption near edge structure (XANES) spectra and the values of the intramolecular distance rBr–Br determined by extended X-ray absorption fine structure (EXAFS). In Group I, prepared from the host carbons heat treated at temperatures higher than 1900 °C, bromine exists in the interlayer space of graphite in the form of Br2 molecules with interaction of the π electrons of graphite. In Group III, from carbon heat treated at 1000 °C, most of the bromine probably reacts with carbon atoms having a dangling bond or functional groups. For Group II, where the host carbons are heat treated at intermediate temperatures, it is likely that bromine exists in undeveloped defects with a unique electronic state. [Copyright &y& Elsevier]